Why Pentax Need a New Mount Now

Currently Pentax have two mount types - K(AF3) for APS-C (and potentially for FF), and Q for a small size sensor.

There is now a clear trend towards mirrorless cameras with big sensors (APS-C, MFT), as they offer DSLR quality in compact package. Current APS-C sensor bodies are comparible in size with 1/1.7"-1/2.3" ones.

Although it is fun to use the Q series, I do not think there is real future for Pentax Q format, unless it stays as a fashion thing (see how many color options are offered for Q-series).

Now we come to the K mount. Pentax K-01 was the first mirrorles with this mount. Although it has a benefit of offereing full compatibility with K-mount lenses (which is great), this camera is clearly off the mainstream as it does not offer similar compact body as competitors. Now K-mount becomes a clear limitation for mirrorless design, and needs to be "upgraded" to fit mirrorless path.

Ideally, this new mount should be suitable for FF. It would probably need to be a bit larger, to make sure that it is suitable for in-body stabilization.

The faster Pentax takes this decision to move to a new mount, the better (but still preserving compatibility with older lenses via a special adaptor).